Hidden Holocene Slip Along the Coastal El Yolki Fault in Central Chile and Its Possible Link With Megathrust Earthquakes

Abstract

Megathrust earthquakes are commonly accompanied by increased upper‐plate seismicity and occasionally triggered fault slip. In Chile, crustal faults slipped during and after the 2010 Maule (M8.8) earthquake. We studied the El Yolki fault (EYOF), a transtensional structure midways the Maule rupture not triggered in 2010. We mapped a Holocene coastal plain using light detection and ranging, which did not reveal surface ruptures. However, the inner‐edge and shoreline angles along the coastal plain as well as 4.3‐ to 4.0‐ka intertidal sediments are back‐tilted on the EYOF footwall block, documenting 10 m of vertical displacement. These deformed markers imply ~2‐mm/year throw rate, and dislocation models a slip rate of 5.6 mm/year for the EYOF. In a 5‐m‐deep trench, the Holocene intertidal sediments onlap to five erosive steps, interpreted as staircase wave‐cut landforms formed by discrete events of relative sea level drop. We tentatively associated these steps with coseismic uplift during EYOF earthquakes between 4.3 and 4.0 ka. The Maule earthquake rupture may be subdivided into three subsegments based on coseismic slip and gravity anomalies. Coulomb stress transfer models predict neutral stress changes at the EYOF during the Maule earthquake but positive changes for a synthetic slip distribution at the central subsegment. If EYOF earthquakes were triggered by megathrust events, their slip distribution was probably focused in the central subsegment. Our study highlights the millennial variability of crustal faulting and the megathrust earthquake cycle in Chile, with global implications for assessing the hazards posed by hidden but potentially seismogenic coastal faults along subduction zones.

TerraceM-2: A Matlab® Interface for Mapping and Modeling Marine and Lacustrine Terraces

“…TerraceM has been designed to close this gap by providing open-source tools to interactively map and model the formation of marine and lacustrine wave-cut terraces using high-resolution topography and Matlab R programming. So far, TerraceM has been used for diverse purposes in different coastal settings worldwide (e.g., Melnick, 2016;Benjelloun, 2017;Jara-Muñoz et al, 2017;Melnick et al, 2017Melnick et al, , 2019Pedoja et al, 2018;Bilbao-Lasa et al, 2019;de Gelder et al, 2019;Jara-Munþoz et al, 2019;Racano et al, 2019). These studies include research topics such as coastal dynamics, paleo-geography, paleo-climate, neotectonics, and earthquake geology, highlighting the broad spectrum of applications and the advantages of applying integrated joint mapping and modeling techniques in the Earth sciences.…”

The cryptic seismic potential of blind faults revealed by off-fault geomorphology, Pichilemu, Chile.

“…Regarding the first scenario, the relation between the coseismic slip distribution during the Maule earthquake and long-term deformation and the observed geophysical characteristics suggests three persistent segments 32,57 ; however, the magnitude of coseismic slip on these segments may vary between cycles 57 . Furthermore, the CFS values on the PIF are negative during the interseismic period that preceded the Maule earthquake 33 (Figs.…”

“…The potential role of heterogeneity in upper-crustal rheology in favouring or limiting surface-reaching faulting is further highlighted by the characteristics of the El Yolki fault, 125 km to the south, which has a similar kinematics and orientation as the PIF 57 . In contrast to the PIF, the El Yolki Fault is not a blind structure and is associated with surface-breaching faulting.…”

“…S11). For the inversion we used the elastic dislocation model and the surface deformation constrained by InSAR, the fault geometry from focal mechanisms of the Pichilemu earthquakes, and a Poisson ratio of 0.25 following previous studies in the region 57,58 . To solve for the slip distribution, we used a least squares minimization determining the bestfit solution that reproduce the InSAR deformation patterns.…”

Marine terraces of the last interglacial period along the Pacific coast of South America (1° N–40° S)

“…Open Access The subduction of bathymetric anomalies has been shown to exert a substantial influence on upper-plate deformation (Fryer and Smoot, 1985;Taylor et al, 1987;Macharé and Ortlieb, 1992;Cloos and Shreve, 1996;Gardner et al, 2013;Wang and Bilek, 2014;Ruh et al, 2016), resulting in temporally and spatially variable fault activity, kinematics, and deformation rates (Mann et al, 1998;Saillard et al, 2011;Morgan and Bangs, 2017;Melnick et al, 2019). When comparing the uplift pattern of MIS-5 marine terraces and the bathymetry of the oceanic plate, we observe that the two long-wavelength structures in this area, on the Manta Peninsula and in the San Juan de Marcona, both coincide with the location of the subducting Nazca and Carnegie ridges, respectively ( Fig.…”